Apparatus and Method for Reducing Acoustical Noise in Synthetic Jets

ABSTRACT

Apparatus and method are provided for reducing acoustical noise when cooling a device, such as a lamp system. The apparatus includes at least a set of a first synthetic jet and a second synthetic jet. The first and second synthetic jets are responsive to respective actuating signals having a phase difference (e.g., 180°) between one another chosen to reduce acoustic noise produced by the first and second synthetic jets when cooling the device.

FIELD

The present invention is generally related to synthetic jets and, moreparticularly, to apparatus and techniques for reducing acoustic noisegenerated due to synthetic jets.

BACKGROUND

It is known to form synthetic jets by periodic suction and ejection offluid out of an orifice in a housing that defines an internal chamber ina synthetic jet ejector. A volume changing mechanism for periodicallychanging the volume within the internal chamber may include a flexiblediaphragm constructed as a wall of the housing. The flexible diaphragmis typically actuated by a piezoelectric actuator or other appropriatemeans.

A control system may be utilized to create time-harmonic motion of thediaphragm. As the diaphragm moves inwardly with respect to the chamber,decreasing the chamber volume, fluid is ejected from the chamber throughthe orifice. As the fluid passes through the orifice, vortices of fluidare formed. These vortices move away from the edges of the orifice undertheir own self-induced velocity. As the diaphragm moves outwardly withrespect to the chamber, increasing the chamber volume, ambient fluid isdrawn from relatively large distances from the orifice into the chamber.Because the exiting vortices are already removed from the edges of theorifice, they are not affected by the ambient fluid being entrained intothe chamber. Thus, as the vortices travel away from the orifice, theysynthesize a jet of fluid, thus called a “synthetic jet,” throughentrainment of the ambient fluid.

A synthetic jet ejector (which may be referred throughout the disclosureas a “synthetic jet”) may be used for thermal management in relativelytight spaces where heat-producing components (e.g., integrated circuit(IC) packages, discrete circuit components, solid state components,etc.) may be disposed and where space for conventional cooling means(e.g., cooling ducts, etc) may be unavailable. Example applications thatmay benefit from synthetic jets may include LED (light emitting diode)lighting systems. Other example applications may include compact mobiledevices, such as cellular phones, pagers, two-way radios, cameras, andthe like.

One known issue in connection with synthetic jets is that duringoperation they may produce relatively high-levels of acoustic noise. Asynthetic jet typically has two natural frequencies at which thesynthetic jet yields an optimum cooling performance. These naturalfrequencies include the structural resonant frequency and the acousticresonance—the Helmholtz-frequency. The structural resonant frequency iscaused at the natural frequency of the structure of the synthetic jet,which consists typically of the synthetic jet plates acting as a massand the elastomeric wall acting as a spring. The Helmholtz frequency ischaracterized by the acoustic resonance of air mass in and out of theorifice of the synthetic jet. The effect is due to the air in thesynthetic jet volume acting as a spring and may be accompanied by a loudtonal noise and a determined vibrational mode if the two modes are notseparated from one another in the frequency domain. Thus, operation of asynthetic jet may result in an acoustically loud noise that could limitor preclude its use for certain applications. In view of the foregoingconsiderations, it would be desirable to provide apparatus and/ortechniques useful for reducing acoustic noise in synthetic jets.

BRIEF DESCRIPTION

In one example embodiment thereof, aspects of the present invention aredirected to apparatus for reducing acoustical noise when cooling adevice with synthetic jets. The apparatus includes at least a set of afirst synthetic jet and a second synthetic jet. The first and secondsynthetic jets are responsive to respective actuating signals having aphase difference between one another chosen to reduce acoustic noiseproduced by the first and second synthetic jets when cooling the device.

In another aspect thereof, a lamp system includes at least a set of afirst synthetic jet and a second synthetic jet. A driver is arranged tosupply respective actuating signals to the first and second syntheticjets. The respective actuating signals have a phase difference betweenone another chosen to reduce acoustic noise produced by the first andsecond synthetic jets. A heat sink is thermally coupled to at least asolid state component of the lamp system arranged to emit light. Thefirst and second synthetic jets are arranged to induce a flow of fluidto cool the heat sink and thereby remove at least some thermal energyproduced by the solid state component when the lamp system is in anoperative condition.

In yet another aspect thereof, a method for reducing acoustical noisewhen cooling a device with synthetic jets comprises: arranging at leasta first synthetic jet and a second synthetic jet to induce a flow offluid for cooling the device; actuating the first and second syntheticjets with respective sinusoidal signals having a phase differencebetween one another and a common frequency value; and selecting thephase difference to reduce acoustic noise produced by the first andsecond synthetic jets when cooling the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cutaway view of one example embodiment of a device(e.g., a LED lighting system), as may be cooled with synthetic jetsadapted to reduce a level of acoustic noise produced by the syntheticjets in accordance with aspects of the present invention.

FIG. 2 illustrates a schematic representation of an example apparatusembodying aspects of the present invention for reducing acoustic noisein synthetic jets.

FIG. 3 illustrates a schematic representation of another exampleapparatus embodying aspects of the present invention for reducingacoustic noise in synthetic jets.

FIG. 4 illustrates an isometric view of a LED lighting system embodyingaspects of the present invention.

FIGS. 5-7 respectively illustrate plots of example comparative levels ofacoustic noise under various example testing arrangements, as may beuseful for comparatively illustrating example noise reduction achievedwhen using synthetic jets embodying aspects of the present invention.

DETAILED DESCRIPTION

In accordance with aspects of the present invention, structural and/oroperational relationships are described herein, as may be useful forreducing acoustic noise in synthetic jets.

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of variousembodiments of the present invention. However, those skilled in the artwill understand that embodiments of the present invention may bepracticed without these specific details, that the present invention isnot limited to the depicted embodiments, and that the present inventionmay be practiced in a variety of alternative embodiments. In otherinstances, well known methods, procedures, and components have not beendescribed in detail.

Furthermore, various operations may be described as multiple discretesteps performed in a manner that is helpful for understandingembodiments of the present invention. However, the order of descriptionshould not be construed as to imply that these operations need beperformed in the order they are presented, nor that they are even orderdependent. Moreover, repeated usage of the phrase “in one embodiment”does not necessarily refer to the same embodiment, although it may. Theterms “comprising”, “including”, “having”, and the like, as used in thepresent application, are intended to be synonymous unless otherwiseindicated.

The adjectives “top” and “bottom” may be used for ease of description,e.g., in reference to the drawings; however, use of such adjectivesshould not be construed as suggestive of spatial limitations. Forexample, in a practical embodiment, structural features and/orcomponents of a given device may be arranged partly in one orientationand partly in another. To avoid linguistic constraints, the adjectives“first” and “second” may be used in lieu of the adjectives “top” and“bottom”, although the terms “first” and “second” could also be used inan ordinal sense.

Aspects of the present invention will be described in the context of aLED (light emitting diode) lighting system. It will be appreciated,however, that such a description should be construed in an example senseand not in a limiting sense being that aspects of the present inventionare not limited to LED lighting systems. It will be now appreciated byone skilled in the art that aspects of the present invention can beapplied to any device or piece of equipment that makes use of two ormore synthetic jets. Other example applications may include compactmobile devices, such as cellular phones, pagers, two-way radios, camerasand the like.

FIG. 1 illustrates a cutaway view of one example of a LED lightingsystem 10 embodying aspects of the present invention. LED lightingsystem 10 includes one or more light sources 12, wherein one or more ofthe light sources may be a solid state component, such as an LED-basedlight source made up of one or more light emitting diodes (LEDs). LEDlighting system 10 may include two or more synthetic jets 14, 16arranged to induce a flow of fluid (e.g., air), as may be effective tocool a heat sink 18 thermally coupled to heat-producing components ofthe lamp system, such as light sources 12 and/or various standardcircuitry 20, 22 commonly used for operation of the lamp system, as willbe readily understood by one skilled in the art. Elaborated descriptionof such standard circuitry is not needed for purposes of understandingand/or practicing the present invention and thus the reader will bespared from such an unnecessary and burdensome description.

The inventors of the present invention have innovatively recognized thatone can actuate one or more sets of synthetic jets 14, 16 withrespective actuating signals having a phase difference between oneanother chosen to reduce acoustic noise produced by synthetic jets 14,16. In one example embodiment, the phase difference may be substantially180°. That is, the phase difference is equal to 180° but for standardtolerances or nominal deviations, as will be readily understood by oneskilled in the art.

In one example embodiment, the 180° phase difference may be obtained byreversing (e.g., flipping) interconnecting leads from a driver 30,(e.g., signal generator and/or amplifier) as may be configured to supplya sinusoidal signal for actuating synthetic jets 14, 16 at a commonfrequency. The description below is based on example embodiments, asshown in FIGS. 2 and 3, where each synthetic jet 14, 16 may comprise afirst actuator 32 and a second actuator 34 (e.g., a top piezoelectricdisk 32 and a bottom piezoelectric disk 34) mechanically coupled tomutually opposing surfaces of an elastomeric wall 31. It will beappreciated by those skilled in the art that aspects of the presentinvention are not limited to any specific structural design of thesynthetic jets, and consequently the foregoing embodiments should beconstrued in an example sense and not in a limiting sense. For readersdesirous of general background information regarding additional examplesof synthetic jets structures, reference is made to U.S. Pat. No.7,688,583, which is assigned in common to the assignee of the presentinvention and is herein incorporated by reference.

In the example shown in FIG. 2, if first actuator 32 of synthetic jet 14is connected to a first signal output terminal 33 of driver 30 (e.g.,terminal labeled with a negative sign (−)), and second actuator 34 ofsynthetic jet 16 is also connected to first terminal 33 of driver 30;then second actuator 34 of synthetic jet 14 would be connected to asecond signal output terminal 35 of driver 30 (terminal labeled with apositive sign (+)) and first actuator 32 of synthetic jet 16 would beconnected to second terminal 35 of driver 30. Therefore, the electricalinterconnections of the actuators may be arranged so that while one jetis ejecting cooling fluid, the second jet is ingesting cooling fluid toprovide an out-of-phase operation, without any phase shiftingelectronics. It will be appreciated by one skilled in the art that inthe context of alternating current (AC) signals, as supplied by driver30, the positive sign and negative sign indications used above are notmeant to indicate voltage polarity but are just example indicators fordenoting an interconnecting arrangement for obtaining the out-of-phaserelationship (180° phase difference) conducive to acoustic noisereduction, in lieu of a conventional in-phase relationship (0° phasedifference), as commonly used in conventional interconnectingarrangements for the of synthetic jets.

It will be appreciated that the phase difference between the actuatingsignals for actuating synthetic jets 14, 16 need not be limited to 180°.It is contemplated that in some applications one could use an adjustablephase shifter 40, as illustrated in FIG. 3, for providing a selectablephase difference, which could be 180°, or any other phase differencevalue, as may be appropriate for a given application. For example, theremay be certain applications where the spatial arrangement of syntheticjets 14, 16 and/or the acoustical properties of the surroundingstructure may call for a phase difference value other than 180° toachieve an optimal noise reduction.

FIG. 4 is an isometric view of LED lighting system 10 where additionalsets of synthetic jets 14, 16, as may be used by the lighting system,are illustrated. In one example embodiment, each pair of adjacentsynthetic jets is arranged to be responsive to respective actuatingsignals having the phase difference chosen to reduce acoustic noise, asdescribed above (out-of-phase relationship). It will be appreciated thatone need not be limited to an arrangement where every adjacent pair ofsynthetic jets is operated in such an out-of-phase relationship. Forexample, one has the flexibility to choose an arrangement where somepairs of adjacent synthetic jets operate in an out-of-phase relationshipand some other pairs of adjacent synthetic jets operate in an in-phaserelationship. It is noted that, although the example embodiments shownin FIGS. 1 and 4 illustrate sets of synthetic jets 14, 16 positionedsubstantially parallel to one another, aspects of the present inventionare not limited to any specific positioning of the synthetic jets.

FIGS. 5-7 respectively illustrate plots of example comparative levels ofacoustic noise for various example testing arrangements, as may beuseful for comparatively illustrating example noise reduction when usingsynthetic jets embodying aspects of the present invention. Each of FIGS.5-7 shows a respective example of a sound level frequency spectrumfor: 1) a single jet; 2) an in-phase pair of jets; and 3) anout-of-phase pair of jets in accordance with aspects of the presentinvention. The plots shown in FIGS. 5-7 correspond to a frequency valueof 160 Hz, 250 Hz and 400 Hz, respectively for the jet actuatingsignals. It is noted that in each example case, the peak noise levelproduced by a pair of out-phase jets in accordance with aspects of thepresent invention single jet is lower than the peak noise level of asingle jet. The overall noise levels across the frequency spectrum forthe various testing arrangements shown in FIGS. 5-7 are listed in thetable below. It will be appreciated that the frequency values listedabove represent example frequency values for the jet actuating signals.In one example embodiment, the frequency value may comprise a range fromapproximately 100 Hz to approximately 500 Hz.

TABLE Noise Level (dB) Single Jet 26.1 39.0 44.8 In-Phase Jets 31.3 44.150.0 Out-of-Phase Jets 24.2 37.8 42.8 Actuating 160 Hz 250 Hz 400 HzFrequency

While various embodiments of the present invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions may be made without departing from the invention herein.Accordingly, it is intended that the invention be limited only by thespirit and scope of the appended claims.

1. Apparatus for reducing acoustical noise when cooling a device withsynthetic jets, the apparatus comprising: at least a set of a firstsynthetic jet and a second synthetic jet, wherein the first and secondsynthetic jets are responsive to respective actuating signals having aphase difference between one another chosen to reduce acoustic noiseproduced by the first and second synthetic jets when cooling the device.2. The apparatus of claim 1, wherein said phase difference comprises avalue of substantially 180°.
 3. The apparatus of claim 2, furthercomprising a driver arranged to supply the respective actuating signalsto the first and second synthetic jets, the actuating signals connectedto actuate respective first and second actuators of said first andsecond synthetic jets in an out-of-phase relationship to provide saidphase difference without any phase-shifting electronics.
 4. Theapparatus of claim 1, further comprising a driver and a phase shiftercoupled to provide the actuating signals to the first and secondsynthetic jets, the actuating signals arranged to actuate respectivefirst and second actuators of said first and second synthetic jets inaccordance with a selectable phase difference provided by the phaseshifter.
 5. The apparatus of claim 1, wherein the first and secondsynthetic jets are positioned substantially parallel to one another. 6.The apparatus of claim 1, further comprising additional sets ofsynthetic jets, wherein each pair of adjacent synthetic jets isresponsive to respective actuating signals having said phase difference.7. The apparatus of claim 1, further comprising additional sets ofsynthetic jets, wherein some pairs of adjacent synthetic jets operate inan out-of-phase relationship and some other pairs of adjacent syntheticjets operate in an in-phase relationship.
 8. The apparatus of claim 1,wherein the device comprises a lamp system that emits light using asolid state component.
 9. The apparatus of claim 1, wherein the solidstate component comprises at least one light emitting diode.
 10. Theapparatus of claim 8, further comprising a heat sink thermally coupledto the solid state component, wherein the first and second syntheticjets are arranged to induce a flow of fluid to cool said heat sink andthereby remove at least some of an amount of thermal energy produced bythe solid state component.
 11. The apparatus of claim 1, wherein therespective actuating signals comprise sinusoidal signals having a commonfrequency value.
 12. The apparatus of claim 1, wherein the frequencyvalue comprises a range from approximately 100 Hz to approximately 500Hz.
 13. A lamp system comprising: at least a set of a first syntheticjet and a second synthetic jet; a driver arranged to supply respectiveactuating signals to the first and second synthetic jets, wherein therespective actuating signals have a phase difference between one anotherchosen to reduce acoustic noise produced by the first and secondsynthetic jets; and a heat sink thermally coupled to at least a solidstate component of the lamp system arranged to emit light, wherein thefirst and second synthetic jets are arranged to induce a flow of fluidto cool said heat sink and thereby remove at least some of an amount ofthermal energy produced by the solid state component when the lampsystem is in an operative condition.
 14. The lamp system of claim 13,wherein said phase difference comprises a value of substantially 180°.15. The lamp system of claim 14, wherein the actuating signals areconnected to actuate respective first and second actuators of said firstand second synthetic jets in an out-of-phase relationship to providesaid phase difference without any phase-shifting electronics.
 16. Thelamp system of claim 13, further comprising a phase shifter coupled tothe driver to provide the actuating signals to the first and secondsynthetic jets, the actuating signals arranged to actuate respectivefirst and second actuators of said first and second synthetic jets inaccordance with a selectable phase difference.
 17. The lamp system ofclaim 13, wherein the first and second synthetic jets are positionedsubstantially parallel to one another.
 18. The lamp system of claim 13,further comprising additional sets of synthetic jets, wherein each pairof adjacent synthetic jets operates in an out-of-phase relationship. 19.The lamp system of claim 13, further comprising additional sets ofsynthetic jets, wherein some pairs of adjacent synthetic jets operate inan out-of-phase relationship and some other pairs of adjacent syntheticjets operate in an in-phase relationship.
 20. The lamp system of claim13, wherein the solid state component comprises at least one lightemitting diode.
 21. The lamp system of claim 13, wherein the respectiveactuating signals comprise sinusoidal signals having a common frequencyvalue.
 22. The lamp system of claim 13, wherein the frequency valuecomprises a range from approximately 100 Hz to approximately 500 Hz. 23.A method for reducing acoustical noise when cooling a device withsynthetic jets, said method comprising: arranging at least a firstsynthetic jet and a second synthetic jet to induce a flow of fluid forcooling the device; actuating the first and second synthetic jets withrespective sinusoidal signals having a phase difference between oneanother and a common frequency value; and selecting the phase differenceto reduce acoustic noise produced by the first and second synthetic jetswhen cooling the device.
 24. The method of claim 23, wherein saidactuating comprises connecting the actuating signals to actuaterespective first and second actuators of said first and second syntheticjets in an out-of-phase relationship to provide said phase differencewithout any phase-shifting electronics.